1. Field of the Invention
This invention relates to a wheel alignment measurement system for motor vehicles.
2. Description of the Prior Art
Some previous wheel alignment measurement systems have been of limited usefulness since they were not able to measure angle data for each of the wheels independently.
Other prior proposals have involved the use of stationary frames, limiting the usefulness of the system because it had to be at a fixed location to which the vehicle was brought.
In British Patent No. 0257144, a versatile wheel alignment measurement system was described, capable of measuring and analyzing data from all four wheels. However, it was a skilled and time-consuming job to set up the system since six angle sensors were required and these had to be connected together by flexible elements stretching between the wheels. Furthermore, the signal outputs from the sensors had to be assigned the correct electrical polarity for analysis purposes. The individual angle sensors were also prone to damage.
In U.S. Pat. No. 4,319,838, it has been proposed to use pairs of symmetrically-disposed electronic signal generators coupled to the vehicle wheels to detect their angular deviation from a line of sight between detectors. The arrangement requires the presence of six detectors, each of which relies on a pair of side-by-side photodiodes to sense the deviation. The results rely solely on calculation based on the readings of the sensors, so misalignment of the diodes or other components may give rise to inaccuracy.
In other prior systems, such as that described in U.S. Pat. No. 4,095,902 signal emitters are used in combination with reflectors, but this is unsatisfactory in that the reflection diminishes the signal strength.